252 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



feet above the mouth of the river. For a couple of miles below the 

 Wisconsin border the shelf is nearly bare, but farther south it carries a 

 gravel deposit 25 to 30 feet in depth. It is probable that the gravel has 

 been removed by stream action from the bare pai't, for that stands below 

 the level of the gravel surface to the south. There has probabl}'' also been 

 considerable erosion of gravel all along the valley, for the surface of the 

 gravel is 50 feet or more below the level of the terraces on the Ohio at 

 Beaver and Phillipsburg. 



The gravel is capped by a silt of pale color, 4 or 5 feet in depth, which 

 may prove to be the equivalent of the lowan loess. Its color is strikingly 

 in contrast with, that of the gravel below it. The gravel is weather stained 

 at top and seems to be much older than the silt. 



As a rule the gravel is poorly assorted and contains much sand, and in 

 places has a clayey matrix. The largest Canadian rocks noted are nearly 

 a foot in diameter. They are deeply weathered, the red granites being 

 usually very rotten. A few striated stones were found in the north part of 

 Beaver Falls, and these have been weathered deeply since the striation 

 occurred. The proportion of Canadian rocks here, as on the Allegheny, is 

 much smaller in this gravel than in gravel of Wisconsin age that lies in the 

 valley below the level of this rock shelf 



Below Beaver Falls the rock shelf is less conspicuous than above that 

 city, though a broad remnant appears on the east side in New Brighton. 

 At this place a clayey deposit appears on the rock shelf, in which stones of 

 various sizes are embedded. 



It being uncertain whether the old drift is exposed on the uplands bor- 

 dering the Beaver Valley outside the limits of the Wisconsin, the relations 

 of the terrace to the drift can not be clearly shown. As yet it is not known 

 whether the border of the old drift lies some distance back beneath the 

 Wisconsin or is practically identical with it in position. There is, however, 

 no question that this gravel, like the similar gravel on the Lower Allegheny 

 and Ohio, has been derived from the old drift and was deposited long before 

 the Wisconsin stage of glaciation. 



The Little Beaver Valley has not been examined by the writer outside 

 the limits of the Wisconsin drift, and nothing has been learned concerning 

 the character of the outwash found along- it. 



